A conventional viscoelastic polisher and a conventional polishing method using the polisher will briefly be described based on FIGS. 14 and 15. FIG. 14 is a plan view of the viscoelastic polisher, and FIG. 15 is a sectional view of the polisher.
In FIGS. 14 and 15, the viscoelastic polisher indicated by 51 includes a viscoelastic layer 52 provided on a surface of a metal base disk 54. The viscoelastic layer 52 has a plurality of annular grooves 53 concentrically formed therein.
A polishing operation is performed by rotating a workpiece to be polished at a predetermined rotation speed and pressing the viscoelastic polisher 51 against the workpiece at a predetermined pressure while supplying an abrasive agent to the viscoelastic layer 52 with the viscoelastic polisher 51 being rotated.
At this time, the abrasive agent held between the viscoelastic layer 52 and the to-be-polished workpiece sinks in the surface of the viscoelastic layer 52 due to the pressure. Therefore, an effective depth to which abrasive particles cut into the to-be-polished workpiece for removal of a surface portion of the workpiece is reduced. That is, the amount of the removed surface portion of the workpiece is reduced. Consequently, the surface of the workpiece is mirror-finished.
Where the polishing operation is performed by utilizing a chemical action, it is advantageous to increase the viscosity and elasticity of the viscoelastic layer 52 for increasing the period and area of contact between the abrasive agent and the to-be-polished workpiece.
Therefore, selection of a material having a higher viscosity and a higher elasticity is more advantageous for quality improvement in the polishing method utilizing the viscoelastic polisher.
In the polishing method in which the polishing operation is thus performed by pressing the to-be-polished workpiece against the viscoelastic polisher 51, the surface of the to-be-polished workpiece is kept in contact with the surface of the viscoelastic polisher, making it difficult to supply the abrasive agent to a portion of the workpiece to be actually polished.
To cope with this, the annular grooves 53 are provided in the viscoelastic layer 52 as shown in FIG. 14 (see, for example, Japanese Unexamined Patent Publication No. HEI9-295255 (1997) and Japanese Unexamined Patent Publication No. HEI10-58331 (1998))
Meanwhile, the conventional polishing method described above has the following drawbacks:    1) Reduction in polishing performance due to reduction of surface viscoelasticity associated with processing of the viscoelastic layer for formation of the grooves;    2) Increase in costs required for the processing for the formation of the grooves; and    3) Change in groove configuration due to wear with time.
Mechanical processing is mainly employed for the formation of the grooves 53 in the viscoelastic layer 52. However, it is difficult to form the grooves 53 in a soft material. Therefore, the surface hardness of the viscoelastic layer 52 is increased by pressing the viscoelastic layer to plastic deformation, and then the viscoelastic layer is processed for the formation of the grooves 53.
Therefore, the viscoelasticity is lost after the formation of the grooves 53, so that the abrasive agent sinking effect is reduced. As a result, the surface of the workpiece being polished is scratched, or the roughness of the finished surface is deteriorated.
The processing for the formation of the grooves 53 increases the costs. Further, the depth of the grooves 53 is reduced with time due to the wear of the surface of the viscoelastic layer 52, so that the effect of the provision of the grooves is reduced with time.
It is therefore an object of the present invention to provide a viscoelastic polisher and a polishing method which ensure easy maintenance of polishing performance and lower costs.